Vapor-liquid contacting devices, such as fractionation trays and packings, are employed to perform an almost endless variety of separations in the petroleum and petrochemical industries. Fractionation trays are used, for example, in the separation of many different hydrocarbons such as paraffins, aromatics and olefins. Vapor-liquid contacting trays are also used to perform gas processing, purification, and absorption.
Vapor-liquid contact has traditionally been conducted in cross flow or counter current contacting devices having an overall downward liquid flow and upward vapor flow. At some point in the apparatus the vapor and liquid phases are brought into contact to allow the vapor and liquid phases to exchange components and approach equilibrium with each other. The vapor and liquid are then separated, moved in the appropriate direction and contacted again with another quantity of the appropriate fluid. In many conventional vapor-liquid contacting devices, vapor and liquid are contacted in a cross flow arrangement at each stage. An alternative apparatus differs from traditional multi-stage contacting systems in that while the overall flow in the apparatus continues to be countercurrent, each stage of actual contacting between the liquid and vapor phases is performed in a co-current mass transfer zone.
During fractional distillation processes using conventional trays, vapor generated at the bottom of the column rises through a large number of small perforations spread over the decking area of the tray, which supports a quantity of liquid. The passage of the vapor through the liquid generates a layer of bubbles referred to as froth. The high surface area of the froth helps to quickly establish a compositional equilibrium between the vapor and liquid phases on the tray. The froth is then allowed to separate into vapor and liquid. During mass transfer, the vapor loses less volatile material to the liquid and thus becomes slightly more volatile as it passes upward through each tray. Simultaneously the concentration of less volatile compounds in the liquid increases as the liquid moves downward from tray to tray. The liquid separates from the froth and travels downward to the next lower tray. This continuous froth formation and vapor-liquid separation is performed on each tray. Vapor-liquid contactors therefore perform the two functions of contacting the rising vapor with liquid and then allowing the two phases to separate and flow in different directions. When the steps are performed a suitable number of times on different trays, the process leads to separation of chemical compounds based upon their relative volatility.
If maldistribution or an unbalanced load of liquid occurs in a conventional vapor-liquid tray contacting apparatus, fluid may not be readily redistributed along the length of the apparatus. Thus, maldistribution of liquid or vapor may propagate from one stage to the next, reducing the capacity and efficiency of the apparatus. Further, unbalanced or maldistributed liquid in contacting stages of a vapor-liquid contacting apparatus may result frequently from operation under non-vertical conditions, i.e., if the vessel itself is rocking or tilted.
Accordingly, it is desirable to provide a vapor-liquid contact apparatus that avoids the issue of maldistribution of liquid in contacting stages. Further, it is desirable to provide vapor-liquid contacting apparatuses and methods with improved contacting and separation efficiency. It is also desirable to provide a vapor-liquid contacting apparatus and method that utilizes vortex contacting stages. Furthermore, other desirable features and characteristics will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.